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110                       . METALLURGY OP IRON" AND STEEL.
proved furnace practice, while difficulties are also avoided by having a large receiver, often called a mixer, into which is poured the melted iron from all tributary furnaces, and in which a mixing or averaging takes place. This receiver is an enlargement of the old American receiving ladle.
SEC. Vli.—Cupola metal.—The cupolas used in steel works measure from 6 to 8 feet internal diameter, while the height should be at least 20 feet. The fuel consumption varies, one pound of coke melting from 11 to 15 pounds of iron. The coke must be as free as possible from sulphur, as the iron, during melting, absorbs this element. With fast running and good coke, this absorption may be "only .02 per cent.; with slow running and bad coke, the sulphur in the iron may be raised .20 per cent, in the cupola. About half of one per cent, of silicon and some manganese are oxidized during melting and also some metallic iron. This loss of iron can be found only by weighing and analyzing the cinder running from the tap-hole. An experiment of this kind on a 24-hour run, melting 400 tons of iron, showed a slag containing 8.77 per cent, of metallic iron, and a loss of iron representing 0.42 per cent, of the pig-iron charged. Other determinations showed a less percentage of iron in the slag.
SEC. VIj.—Factors affecting the calorific history.—Until within a few years, it was thought necessary to have from 2.0 to 2.5 per cent, of silicon in the metal as it entered the converter, but the general practice at the present time is to have from 1.0 to 1.5 per cent., although it is feasible to operate with a content of from 0.6 to 0.8 per cent. This reduction of calorific power has been made •practicable by several small improvements:
(1)   Fast running, the iron never standing long enough to cool, and the steel ladles and vessels always being hot.
(2)   Quick blowing, the radiation from the vessel being  decreased, and the time lessened during which the idle vessel is cooling.
(3)   Good bottoms and linings, the scorified material being reduced, and delays for repairs avoided.
(4)   Quick changes of bottoms, and less cooling of the vessels.
(5)   Blowing with the vessel partly tipped over when the charge is cool, rendering less necessary an excess of heat-producing elements as a provision against delays or change of bottoms.